1. Field of the Invention
The present invention relates to a sheet transformer suitable for a thin sheet type power supply transformer for use in, for example, telephone exchanges, industrial inverters, thin type displays and the like.
2. Description of the Related Art
Generally, a transformer having a structure as shown in FIG. 15 is well known. In this transformer, conductive wires are wound around parallel portions of a rectangular core 1 so as to form a primary coil 2 and a secondary coil 3. A power supply 4 is connected to both terminals of the primary coil 2 through a switch terminal 5 such as a MOS-FET, or the like. Further, one terminal of the secondary coil 3 is grounded and a load 6 is connected to the other terminal through a stabilizing circuit. A voltage applied to the primary coil 2 is converted to a predetermined voltage by dielectric action between the primary coil 2 and secondary coil 3 and applied to the load 6. This type of transformer is called a fly-back transformer.
In such a transformer, a problem occurs when the voltage applied to the primary coil 2 induces a voltage in the secondary coil 3. A voltage difference in time change occurs between the primary coil 2 and the secondary coil 3 (i.e., a voltage difference between the primary coil 2 and the secondary coil 3 according to the change of time) resulting in the generation of noise.